Abstract: Myocardial stunning is present following ischemic insults associated with elective cardiac arrest during the majority of cardiac surgeries and significantly contributes to patient morbidity and mortality. During surgery, cardioplegia solutions provide significant cardioprotection from what would otherwise be lethal ischemic injury. However, there is still significant injury during these procedures to the myocardial tissue. This grant seeks to determine 1) the mechanism of cardioprotection associated with activation of a mitochondrial K+ channel (BKCa) and if driving activation will mitigate myocardial stunning associated with ischemic insults during cardiac surgery, and 2) if novel strategies to promote mitochondrial reorganization and function are viable therapeutic strategies. The mechanism of mitochondrial K+-mediated cardioprotection is currently unknown. We present preliminary data, that activators or overexpression of active BKCa channels improves LV function and hemodynamics following ischemic injury associated with isolated cell and animal models of cardioplegic arrest. We also present novel evidence that BKCa activation may improve cardioprotection through alterations in mitochondrial structural proteins and increase the formation of electron transport chain supercomplexes, thereby providing more efficient cellular respiration, and decreased reactive oxygen species generation. The current proposal will investigate the novel mechanism of mitochondrial K+ mediated cardioprotection with specific focus on K+-dependent modulation of mitochondrial cristae junction protein complexes, enhanced mitochondrial supercomplex formation, improved respiration, and decreased ROS. In addition, there is a strong effort towards translation of these studies, with verification of the relevant findings in a pre-clinical large animal model of CP/CPB and definition of the proposed pathological insult in human heart tissue before and after cardiac surgery. The potential elucidation of this mechanism will have implication for ischemic injury and numerous other myocardial metabolic alterations. The proposal is in three specific aims: I) Determine the role of respiratory supercomplexes and cristae remodeling in BKCa-mediated enhanced myocardial protection in vitro. The mechanism of BKCa-mediated cardioprotection (respiration, respiratory supercomplex formation, ATP generation, superoxide production, etc...) will be evaluated using isolated myocytes with genetic and pharmacologic manipulation. II) Determine if BKCa-mediated supercomplex formation enhances cardiac contractile function and cardioprotection following cardioplegic arrest and reperfusion ex vivo. Mouse isolated hearts will be subjected to ischemic cardioplegic arrest and reperfusion with and without BKCa channel pharmacologic activators and genetic interventions. III) Determine if similar pathological mechanisms are present in humans undergoing CP/CPB using myocardial tissue samples before and after bypass, and finally, determine if BKCa activation promotes supercomplex formaton and reduces myocardial stunning in a clinically relevant diseased large animal model of CP/CPB.